Protective tolerance to fungi: the role of IL-10 and tryptophan catabolism

The pro-inflammatory–anti-inflammatory signaling balance is required for successful host–fungus interactions. The occurrence and interference of regulatory T (T-reg) cells in fungal infections offers a valuable framework for events that occur at the host–fungus interface. Control of both the class and magnitude of the immune response might confer an evolutionary advantage whereby the host effectively fights infection but limits collateral immunopathology. Alternatively, fungus-induced immunosuppression could be a powerful immunoevasion strategy for the invading pathogen. Discovery of T-reg cells as a source of IL-10 might contribute to a better understanding of the opposing functions and variable levels of production of this prototypic immunoregulatory cytokine in fungal infections and inflammatory diseases. T-reg cells, however, might also represent an additional mechanistic level at which host responses are subverted by fungi.